London police are warning the public that cocaine seized in November contained the deadly opioid fentanyl.

Health Canada tests confirmed the presence of fentanyl — an opioid 100 times more powerful than morphine — in drugs found on a 33-year-old London man after he was arrested.

“This is the first time in London that both cocaine and fentanyl were discovered in the same sample,” police said in a news release Sunday.

“It is not confirmed if the drugs were intentionally or inadvertently mixed.”

The man, whose case is before the courts, had crack cocaine and fentanyl, police said.

He was charged with several offences, including possession of a controlled substance,

Police warned that fentanyl and other dangerous opioids can be mixed with other drugs such as cocaine, heroin, ecstacy and oxycodone.

“Trying any drug — even just one time — could kill the user if it’s mixed with fentanyl or carfentanil,” the police statement said.

The arrival of fentanyl and carfentanil, a similar, even more powerful opioid, is forcing health officials and police to react on a number of fronts.

The Middlesex-London Health Unit plans to open a temporary overdose prevention site as early as this month.

The temporary site would have supervision, clean needles and the opioid overdose antitode naloxone. The facility is needed because of the toll opioids are taking on users, health officials and frontline workers say.

Middlesex-London medical officer of health Chris Mackie has said more than one temporary site could open.

The health unit also is continuing with plans to open a permanent supervised drug consumption site in London.

The Ontario government is offering naloxone to all of the province’s police and fire departments as part of an effort to combat the opioid crisis.

London police are moving ahead with plans to issue naloxone to officers to protect them if they come in contact with opioids.

The warned issued Sunday by London police was the second opioid-related warning within two months.

In November, police warned carfentanil — a synthetic opioid 10,000 times more powerful than morphine — was found in seized drugs.

A small amount of carfentanil powder, as little as two milligrams, can be lethal through inhalation, ingestion or absorption through the skin.